Solvent extraction of drying oils



Patented July 9, 1946 SOLVENT EXTRACTION OF DRYDIG OILS Olive Sue Ransom, New York, and Milton Zucker, New Rochelle, N. Y., assignors to Interchemical Corporation, New York, N. Y., a corporationof Ohio No Drawing. Application May 15, 1942, Serial No. 443,080

3 Claims. (Cl. 260-4285) This invention relates to the treatment of fatty oils of the drying and semi-drying types, and it is especially concerned with the separation of the drying portions of such oils from the non-drying portions by means of solvent extraction.

All naturally occurring fatty oils are mixtures of the glycerides of various higher fatty acids, both saturated and unsaturated, and they are classifi-ed approximately as drying, semi-drying or non-drying according to their ability to become hard and resinous upon exposure to heat or air, due to polymerization or oxidation of the highly unsaturated fatty acid constituents. That is, the more "drying" an oil is, the higher is its percentage of the very unsaturated, or polymerizing,

constituents, and the more valuable the oil may be for use in making varnishes and other protective coating materials. In addition these oils contain small amounts of sterols, hydrocarbons, waxes, other esters, oil-soluble vitamins and phosphatides.

It'has been proposed to separate these oils into two or more components, one rich in the highly unsaturated glycerides and the other rich in the saturated glycerides, by means of selective solvent extraction, inasmuch as the highly unsaturated glycerides, if at least partly polymerized, are essentially insoluble in certain organic solvents. The highly unsaturated components of the oil may be partly polymerized by heating the oil until its viscosity increases (known as bodying the oil). As is well known, the selectionof the particular solvent or extractant for accomplishing such a separation is of paramount importance, as the various organic liquids and combinations thereof which are partly miscible with these oils differ widely in ability to separate the drying from the non-drying components of the oils, and there is, of course, no way of predicting or determining in advance of actual trial the usefulness of any particular organic solvent or combination. In the Behr U. S. Patents Nos. 2,166,103, issued July 18, 1939, and 2,239,692, issued April 29, 1941, there is disclosed a method for the selective solvent extraction of these oils employing, as the solvent, various ketones and higher alcohols, especially acetone, and according to the Eibner U. S. Patent No. 1,934,297 the selective solvent may be a mixture of a higher alcohol which is a solvent for the unsaturated components, such as amyl alcohol, and a non-solvent for the unsaturated oil component.

Oils which have had their non-drying components extracted by means of the various solvents disclosed in the above patents generally form more or less brittle films on drying. This is particularly true of acetone extracted oils. Although the brittleness can be reduced by retaining part of the non-drying components in the treated oil, the fast drying properties of the oil are also reduced, and in some cases the oil will not dry to a tack free film in a reasonable length of time.

This invention provides a=method for the selective solvent extraction of naturally occurring fatty oils wherein the drying components are concentrated and separated from the non-drying components to produce fast drying oils which dry to tack free films which are not as brittle as those made from drying oils treated with conventional solvents. Similarly, the invention provides a new selective solvent which is capable of producing fastdrying oils of a given viscosity in greater yield than has been obtained heretofore, and the selective characteristics of the solvent may be adjusted at will, within certain limits.

The new selective solvent on which the process of this invention depends is a mixture of ethanol and ethyl acetate. Neither of these two liquids can be used alone because the ethanol will not appreciably dissolve any of the oil and the ethyl acetate is too powerful a solvent. In practice it has been found desirable to limit the proportions ofethanol and ethyl acetate in order to maintain an elficient extraction process, and ordinarily the proportion should be Within the limits of about 3 to 5 volumes of ethanol to 1 volume of of ethyl acetate.

However, the proportion of ethanol to ethyl acetate which gives the most efficient extraction depends partly on the type of oil being processed and partly on the degree to which the oil has been bodied or polymerized (as may be indicated by viscosity).

It is essentialthat the solvent mixture be anhydrous or substantially so, as the presence of Water in even the small amount encountered in the ethanol-water azeotropic mixture (where the solvent contains substantial quantities of ethanol) is sufficient to preventthe separation desired.

In order that the invention may be more clearly understood, the following examples of fish oil and vegetable oil extractions are given by way of illustration Example 1 A sardine oil was heat bodied according to standard pactice until its viscosity had increased to 14.7 poises at 25 C. Samples of the bodied oil were extracted with difierent proportions of The ethanol used was denatured with 5% ethyl acetate, 5% methanol and 1% petroleum-distil late, by volume. The denaturants caused a slight modification in the properties of the solvent mix ture over those obtained when using pure ethar nol. The yields and viscosities of the treated oils are given in the following table in which the figure in the solvent column refers to the volume of solvent used for each volume of unextracted oil:

Yield 4 ethanol: (volume Viscosity Acetone 1 ethyl per cent of (in poises.

acetate original at 25 0.) oil) Although the acetone produced an extracted.

oil of greater viscosity than did an equal volume of the ethanol-ethyl acetate mixture, the yield was less and the products formed more brittle,

films on drying.

' Example 2 A similar test was made using linseed oil heat bodied in accordance with standard practice to a viscosity of 19.1 poises at 25 C. The results are as follows:

Yield 4 ethanol (volume Yiscosity Acetone 1 ethyl per cent of (in poises acetate original at 25 0.) oil) Like the test on the sardine oil, the oil extracted. with acetone was of greater viscosity than that extracted with a similar volume of the ethanol-ethyl acetate mixture, the yield was less and it formed more brittle films on drying.

Although the degree to which the raw oil should be bodied, or the highly unsaturated components polymerized, depends on the particular characteristics desired in the treated oil, it is necessary that the raw oil be polymerized to some extent, in order for the selective extraction to take place. I

Mixtures of. other alcohols and esters have been tested for use as selective solvents, but none has been discovered which has the universal ability to produce good yields of fast drying oils which form comparatively non-brittle films, as

compared to the ethanol-ethyl acetate mixture.

Instead of batch solvent extraction, as indicated in the examples, a continuous extraction process may be employed, using countercurrent flow and continuous removal of solvent from the drying and non-drying oil fractions by distillation and return of the solvent in contact with fresh oil. Also, any of the vegetable oils, such as linseed, tung, soya, perilla, walnut and the like, and marine oils, such as sardine, menhaden, pilchard and similar fish oils, which contain polymerizable constituents may be treated in the manner described to yield oil fractions of superior drying properties.

We claim:

1. Method for treating heat bodied polymerized vegetable and marine drying oils to obtain oil fractions therefrom of increased drying properties which comprises, mixing such oil with a substantially anhydrous organic solvent consisting essentially of about 3 to 5 volumes of ethan01 to 1 volume of ethyl acetate, permitting the mixture of solvent and oil to separate into two layers, each layer containing an oily constituent, separating the two layers and removing the contained solvent from the layer containing a predominance of the polymerized constituents having increased drying properties- 2. Method of treating heat bodied polymerized vegetable and marine drying oils to obtain an oil fraction therefrom of increased drying properties which comprises, mixing such oil with a substantially anhydrous organic solvent consisting essentially of a mixture of about four volumes of ethanol and about one volume of ethyl acetate, permitting the mixture of oil and solvent to separate into two layers and recovering the oil fraction from the layer containing a predominance of the polymerized constituents having increased drying properties.

3. Method for treating heat bodied polymerized drying oils containing drying and non-drying constituents which comprises removing from said oils at least a portion of said non-drying constituents by bringing said oil into intimate contact with a substantially anhydrous organic solvent consisting essentially of about 3 to 5 volumes of ethanol to 1 volume of ethyl acetate.

OLIVE son RANSOM. MILTON ZUCKER. 

